Polarizing Plate and Image Display Device Comprising Same

ABSTRACT

A polarizing plate includes a polarizer; and a protective layer provided on one surface or both surfaces of the polarizer directly adjoining the polarizer, wherein the protective layer is a cured material of a photocurable composition for a polarizing plate protective layer comprising an epoxy compound and an oxetane-based compound. An image display device includes the polarizing plate.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a national stage entry under U.S.C. § 371 of International Application No. PCT/KR2018/011187 filed on Sep. 20, 2018, which claims priority to Korean Patent Application No. 10-2017-0122686, filed with the Korean Intellectual Property Office on Sep. 22, 2017, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present specification relates to a polarizing plate and an image display device comprising the same.

BACKGROUND ART

Existing polarizing plates for a liquid crystal display device uses a general polyvinyl alcohol-based polarizer, and have a constitution of attaching a protective film such as triacetyl cellulose (TAC) on at least one side surface of the polarizer.

In a recent polarizing plate market, demands for low light leakage and thinning have increased, and in order to satisfy these properties, a method of directly forming a protective film on a polarizer has been examined instead of using an existing protective substrate formed as a film in advance.

However, when directly forming a protective film on an existing elongation-type polyvinyl alcohol-based polarizer, a problem of the polarizer being torn by stress generated from polarizer shrinkage at a high temperature has been difficult to resolve compared to when using a protective substrate on both surfaces as in the art.

DISCLOSURE Technical Problem

The present specification is directed to providing a polarizing plate and an image display device comprising the same.

Technical Solution

One embodiment of the present specification provides a polarizing plate comprising a polarizer; and a protective layer provided on one surface or both surfaces of the polarizer directly adjoining the polarizer, wherein the protective layer is a cured material of a photocurable composition for a polarizing plate protective layer comprising an epoxy compound and an oxetane-based compound, the following Equation 1 is satisfied in a spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer, the protective layer has a thickness of 4 μm to 11 μm, and the following Equation 1 is satisfied in a spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer.

$\begin{matrix} {0.9 \leq \frac{I_{e}}{I_{a} + I_{e}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \end{matrix}$

In Equation 1,

I_(e) is a ratio of peak intensity at 920 cm⁻¹ to 900 cm⁻¹ with respect to peak intensity at 1740 cm⁻¹ to 1700 cm⁻¹ in the spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer, and

I_(a) is peak intensity at 1420 cm⁻¹ to 1380 cm⁻¹ with respect to peak intensity at 1740 cm⁻¹ to 1700 cm⁻¹ in the spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer.

Another embodiment of the present specification provides an image display device comprising the above-described polarizing plate.

Advantageous Effects

A polarizing plate according to one embodiment of the present specification replaces an existing base layer provided with an adhering layer in between with one coating layer, and thereby has advantages of accomplishing thinning and weight lightening of the polarizing plate and minimizing costs and processes.

A polarizing plate according to one embodiment of the present specification has an advantage of having a small or almost no phase difference.

A polarizing plate according to one embodiment of the present specification has an advantage of, by comprising a protective layer having high tensile modulus and storage modulus, not causing significant shrinkage when curing a photocurable composition for a protective layer in order to form a protective layer.

In addition, there is an advantage in that light leakage caused by shrinkage or expansion of a polarizer can be suppressed even under a high temperature or high humidity environment.

In addition, tensile modulus and tensile modulus of the protective layer are high, and there is an advantage of having high durability even when a separate protective film is not included on the protective layer.

A polarizing plate according to one embodiment of the present specification has excellent durability under a high temperature environment, and has an advantage of suppressing light leakage when used in a liquid crystal display device having a large area.

In addition, a polarizing plate according to one embodiment of the present specification is capable of minimizing the occurrences of yellowing of a protective layer.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a polarizing plate according to one embodiment of the present specification.

FIG. 2 illustrates a polarizing plate according to another embodiment of the present specification.

FIG. 3 illustrates a polarizing plate according to still another embodiment of the present specification.

FIG. 4 is a sectional diagram illustrating one example of an image display device according to one embodiment of the present specification.

FIG. 5 is an FTIR spectrum of a polarizing plate for a protective layer of Comparative Example 8.

FIG. 6 is an FTIR spectrum of a polarizing plate for a protective layer of Example 1.

REFERENCE NUMERAL

-   -   10: Polarizer     -   20: Protective Layer     -   30: Protective Film     -   40: Gluing Layer     -   100: Polarizing Plate     -   200: Liquid Crystal Panel

MODE FOR DISCLOSURE

Herein, the present disclosure will be described.

In the present specification, a description of a certain member being placed “on” another member comprises not only a case of the one member adjoining the other member but a case of still another member being present between the two members.

In the present specification, a description of a certain part “comprising” certain constituents means capable of further comprising other constituents, and does not exclude other constituents unless particularly stated on the contrary.

In the present specification, FTIR means Fourier transform infrared spectroscopy, and a Varian 3100 FT-IR (manufactured by Varian, Inc.) may be used in measurements.

In the present specification, “peak intensity at 1740 cm⁻¹ to 1700 cm⁻¹” is peak intensity for a C═O bond of a protective layer, and is used for normalizing other peak intensity.

In the present specification, “peak intensity at 920 cm⁻¹ to 900 cm⁻¹” is peak intensity for a C—O bond of an oxirane group (stretching C—O of oxirane group) of an oxetane compound of a protective layer.

In the present specification, “peak intensity at 1420 cm⁻¹ to 1380 cm⁻¹” is peak intensity for a ═CH—H bond of an acrylic compound (═CH—H bond of acrylate) of a protective layer, I_(e) represents the presence of an epoxy group of the protective layer, and I_(a) represents the presence of an acrylate group of the protective layer.

In the present specification, the peak intensity corresponds to a peak area of an FTIR spectrum. For example, the peak area may be derived using a direct integration method. In addition, assuming one peak of the FTIR spectrum having Gaussian distribution, the peak area may be expressed by the product of the height and the half value width of the peak.

In the present specification, the peak intensity may be each measured before/after curing a protective layer composition.

Hereinafter, a polarizing plate according to one embodiment of the present specification will be described.

According to FIG. 1, the polarizing plate according to one embodiment of the present specification comprises a polarizer (10); and a protective layer (20) provided on one surface or both surfaces of the polarizer (10) directly adjoining the polarizer.

One embodiment of the present specification provides a polarizing plate comprising a polarizer; and a protective layer provided on one surface or both surfaces of the polarizer directly adjoining the polarizer, wherein the protective layer is a cured material of a photocurable composition for a polarizing plate protective layer comprising an epoxy compound and an oxetane-based compound, the following Equation 1 is satisfied in a spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer, the protective layer has a thickness of 4 μm to 11 μm, and the following Equation 1 is satisfied in a spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer.

$\begin{matrix} {0.9 \leq \frac{I_{e}}{I_{a} + I_{e}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \end{matrix}$

In Equation 1,

I_(e) is a ratio of peak intensity at 920 cm⁻¹ to 900 cm⁻¹ with respect to peak intensity at 1740 cm⁻¹ to 1700 cm⁻¹ in the spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer, and

I_(a) is peak intensity at 1420 cm⁻¹ to 1380 cm⁻¹ with respect to peak intensity at 1740 cm⁻¹ to 1700 cm⁻¹ in the spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer. Satisfying Equation 1 means the protective layer of the polarizing plate hardly comprising an acrylate group. This is effective in enhancing toughness and hardness of the protective layer compared to when the protective layer comprises an acrylate group or an acrylic compound.

In addition, stress is generated on the polarizer when elongating the polarizer or the polarizing plate, and cracks occur on the polarizer when exposing the polarizing plate to a high temperature. A protective layer is introduced to the polarizer for preventing this phenomenon, and when the protective layer comprises an acrylate group or an acrylic compound, the protective layer may not effectively protect the polarizer causing a problem of crack occurrences on the polarizer at a high temperature.

Meanwhile, when the protective layer does not comprise an acrylate group or an acrylic compound and comprises an epoxy compound and an oxetane compound, the protective layer effectively protects the polarizer, which effectively suppresses crack occurrences on the polarizer at a high temperature.

In addition, in the polarizing plate according to one embodiment of the present specification, the protective layer is a cured material of a photocurable composition for a polarizing plate protective layer comprising an epoxy compound and an oxetane-based compound, and by controlling the protective layer to have a thickness of 4 μm to 11 μm, occurrences of yellowing of the polarizing plate or the protective layer may be effectively prevented.

In one embodiment of the present specification, [Equation 1] may be represented by the following Equation 1-1 or Equation 1-2. This is effective in enhancing toughness and hardness of the protective layer compared to when the protective layer comprises an acrylate group or an acrylic compound.

$\begin{matrix} {0.95 \leq \frac{I_{e}}{I_{a} + I_{e}}} & \left\lbrack {{Equation}\mspace{14mu} 1\text{-}1} \right\rbrack \\ {0.98 \leq \frac{I_{e}}{I_{a} + I_{e}}} & \left\lbrack {{Equation}\mspace{14mu} 1\text{-}2} \right\rbrack \end{matrix}$

In one embodiment of the present specification, the protective layer has a thickness of 4 μm to 11 μm, preferably 5 μm to 10 μm, and more preferably 6 μm to 8 μm. The protective layer thickness being smaller than the above-mentioned range may cause a concern of decreasing hardness or high temperature durability of the protective layer, and the thickness being larger than the above-mentioned range has a problem in that it is not proper in terms of thinning of the polarizing plate, and yellowness of the protective layer greatly increases. Accordingly, by controlling the protective layer to have a thickness in the above-mentioned range, the polarizing plate of the present specification is effective in suppressing the increase in the yellowness of the protective layer.

In one embodiment of the present specification, the protective layer may have yellowness (Yp) of 1 or less, preferably 0.9 or less, and more preferably 0.8 or less. The yellowness satisfying the above-mentioned numerical range has an advantage of suppressing decline in the optical properties of the polarizing plate caused by yellowing occurring in the protective layer.

In one embodiment of the present specification, a change in yellowness (ΔYp) calculated by the following Equation 2 is 1 or less, preferably 0.9 or less, and more preferably 0.8 or less.

Change in yellowness: ΔYp=Ybf−Ybi  [Equation 2]

In Equation 2, Ybi is yellowness of the polarizer, and Ybf is yellowness of the protective layer when leaving the polarizing plate unattended for 48 hours under a condition of 25° C. and 40% relative humidity.

In the present specification, Ybi is yellowness of the polarizer, and means a value measuring yellowness of the polarizer itself without providing a protective layer.

In the present specification, ΔYp is a difference value between yellowness of the protective layer-formed polarizing plate (Ybf) and yellowness of the polarizing plate without forming the protective layer (Ybi), and means yellowness (Yp) of the protective layer itself. In addition, yellowness of the polarizing plate without forming the protective layer (Ybi) may use a result of calculating yellowness of a polarizer itself without protective layer lamination.

In the present specification, the yellowness may be measured using a ray spectrometer (V-7100, manufactured by JASCO International Co., Ltd.).

When directly forming a protective film on an existing polyvinyl alcohol-based elongation-type polyvinyl alcohol-based polarizer, a problem of the polarizer being torn by stress generated from polarizer shrinkage at a high temperature has been difficult to resolve compared to when using a protective substrate on both surfaces as in the art. In addition, in order to prevent a problem of optical property decline in the polarizing plate caused by the protective substrate, properties of no phase difference and no yellowing have been required.

Accordingly, in order to directly form a protective film on a polarizer, properties sufficient to endure stress caused by polarizer shrinkage at a high temperature are required. As a protective film satisfying such properties, a UV curable cation-based coating layer is normally used. A photoinitiator and a photosensitizer are normally used in order to enhance the degree of curing in the cation-based coating layer, and in such a process, a problem of optical property decline occurs in the polarizing plate due to yellowing of the cured material.

In one embodiment of the present specification, the protective layer may have a thermal expansion coefficient of 100 ppm/K or less, 85 ppm/K or less, greater than or equal to 10 ppm/K and less than or equal to 100 ppm/K, or greater than or equal to 10 ppm/K and less than or equal to 85 ppm/K at 80° C.

In one embodiment of the present specification, the protective layer may have a thermal expansion coefficient of 100 ppm/K or less, 85 ppm/K or less, greater than or equal to 10 ppm/K and less than or equal to 100 ppm/K, or greater than or equal to 10 ppm/K and less than or equal to 85 ppm/K when measured at a temperature of lower than 80° C.

In one embodiment of the present specification, the protective layer may have a thermal expansion coefficient of 100 ppm/K or less, 85 ppm/K or less, greater than or equal to 10 ppm/K and less than or equal to 100 ppm/K, or greater than or equal to 10 ppm/K and less than or equal to 85 ppm/K when measured at a temperature of higher than 40° C. and lower than 80° C.

In one embodiment of the present specification, the protective layer may have a thermal expansion coefficient of 100 ppm/K or less, 85 ppm/K or less, greater than or equal to 10 ppm/K and less than or equal to 100 ppm/K, or greater than or equal to 10 ppm/K and less than or equal to 85 ppm/K at 70° C.

In one embodiment of the present specification, the protective layer may have a thermal expansion coefficient of 100 ppm/K or less, 85 ppm/K or less, greater than or equal to 10 ppm/K and less than or equal to 100 ppm/K, or greater than or equal to 10 ppm/K and less than or equal to 85 ppm/K at 60° C.

The thermal expansion coefficient of the protective layer satisfying the above-mentioned range has an advantage of effectively suppressing crack occurrences on the polarizing plate under a thermal shock environment.

The method of measuring the thermal expansion coefficient is not particularly limited, and for example, a cured specimen having a thickness of 50 μm prepared by coating a photocurable composition having the same composition as the protective layer is cut to a size of a 6 mm width and a 10 mm length, and while maintaining a tension load at 0.05 N, changes in the length are measured as the temperature is raised up to 150° C. starting from 30° C. Herein, the temperature raising rate is 5° C./min, and after completing the measurement, a thermal expansion coefficient (CTE) value is calculated as a length changed from 40° C. to a target temperature. The target temperature is a temperature of 80° C. or lower than 80° C., and for example, is 70° C. or 60° C.

In one embodiment of the present specification, the protective layer may have a glass transition temperature (Tg) of higher than or equal to 90° C. and lower than or equal to 170° C., preferably higher than or equal to 100° C. and lower than or equal to 150° C., and more preferably higher than or equal to 100° C. and lower than or equal to 130° C. The glass transition temperature of the protective layer satisfying the above-mentioned numerical range has an advantage of maintaining properties of the protective layer under a high temperature environment.

The glass transition temperature of the protective layer is measured through differential scanning calorimetry (DSC) after coating on a release film (for example, a polyethylene terephthalate film) to a thickness of 6 μm to 7 μm, curing the result by irradiating ultraviolet rays, then removing the releasing film, and taking 5 mg to 10 mg of the specimen. Herein, as for the measurement temperature, heat flow is measured while raising the temperature up to 150° C. starting from the temperature of 25° C. at a temperature raising rate of 5° C./min, and a glass transition temperature at the infection point is measured.

Protective Layer

The polarizing plate according to one embodiment of the present specification comprises a protective layer directly formed on any one surface or both surfaces of the polarizer. Since the polarizer is vulnerable to external shock, common polarizing plates comprise a polarizer and, on both surfaces thereof, a protective film adhered with an adhesive. This has a problem in that the polarizing plate thickness increases as the thickness of the protective film attached.

However, by the polarizing plate according to one embodiment of the present specification comprising a protective layer provided on one surface or both surfaces of the polarizer, a separate protective film is not included, or a protective film is included on just one surface of the polarizer significantly decreasing the thickness, and a polarizing plate capable of cost savings is obtained. As a result, a thin-filmed and light-weighted image display device may be obtained.

In one embodiment of the present specification, the protective layer is for supporting and protecting the polarizer, and may be formed using methods well-known in the art.

Each of the protective layers of the polarizing plate according to one embodiment of the present specification may direct adjoin the polarizer. Directly adjoining one surface or both surfaces of the polarizer means the polarizer and the protective layer adjoining each other without an adhesive layer provided in between. In other words, by the protective layer according to the present specification being directly formed on the polarizer without an adhesive layer, a thin polarizing plate may be provided.

Each of the protective layers of the polarizing plate according to one embodiment of the present specification may direct adjoin both surfaces of the polarizer.

In one embodiment of the present specification, the protective layer may be provided on both surfaces of the polarizer.

The protective layer of the polarizing plate according to one embodiment of the present specification is effective in suppressing crack occurrences on the polarizer under a harsh environment while protecting the polarizer.

In one embodiment of the present specification, the protective layer has storage modulus of 1,500 MPa or greater, greater than or equal to 1,500 MPa and less than or equal to 10,000 MPa, preferably greater than or equal to 1800 MPa and less than or equal to 8,000 MPa, and more preferably greater than or equal to 2,000 MPa and less than or equal to 7,000 MPa at 80° C. When the storage modulus of the protective layer satisfies the above-mentioned numerical range, stress applied to the polarizer is effectively suppressed, which is effective in effectively suppressing crack occurrences on the polarizer caused by the shrinkage or expansion of the polarizer under a high temperature or high humidity environment. In addition, adhesive strength for the polarizer is enhanced. As a result, by suppressing shrinkage and expansion of the polarizing plate at a high temperature, occurrences of light leakage may be prevented when using the polarizing plate in a liquid crystal panel and the like, and excellent adhesive strength is obtained. Particularly, the protective layer having storage modulus of greater than or equal to 2,000 MPa and less than or equal to 7,000 MPa at 80° C. has an advantage of very effectively suppressing crack occurrences on the polarizer by effectively suppressing polarizing plate shrinkage at a high temperature.

Storage modulus of the protective layer is measured through DMA after coating a photocurable composition having the same composition as the protective layer on a release film (for example, polyethylene terephthalate film) to a thickness of 50 μm, curing the result by irradiating ultraviolet rays under a condition of light intensity being 1000 mJ/cm² or greater, then removing the release film, and laser cutting the specimen to a certain size. Herein, the storage modulus is measured when constantly tensioning with 10% strain while, as the measurement temperature, raising the temperature up to 160° C. starting from −30° C. at a temperature raising rate of 5° C./min, and a storage modulus value at 80° C. is recorded.

In one embodiment of the present specification, the protective layer has tensile modulus of 1,700 MPa or greater, preferably 1,800 MPa or greater, and more preferably 2,000 MPa or greater at 25° C. When the tensile modulus of the protective layer satisfies the above-mentioned numerical range, stress applied to the polarizer is effectively suppressed, which is effective in effectively suppressing crack occurrences on the polarizer caused by the shrinkage or expansion of the polarizer under a high temperature or high humidity environment. In addition, adhesive strength for the polarizer is enhanced. As a result, by suppressing shrinkage and expansion of the polarizing plate at a high temperature, occurrences of light leakage may be prevented when using the polarizing plate in a liquid crystal panel and the like, and excellent adhesive strength is obtained.

Tensile modulus of the protective layer is measured by a universal testing machine (UTM) after coating a composition having the same composition as the protective layer on a release film (for example, polyethylene terephthalate film) to a thickness of 100 μm, curing the result by irradiating ultraviolet rays under a condition of light intensity being 1000 mJ/cm² or greater, then removing the release film, and laser cutting the specimen to a 10 mm width. Herein, the tensile modulus is obtained through a stress-strain (S-S) curve obtained by constantly tensioning with a measurement length of 50 mm and a tension rate of 50 mm/min at a measurement temperature of 25° C. The tensile modulus is obtained by multiplying the initial slope value of the S-S curve by 100.

In one embodiment of the present specification, when leaving the polarizing plate unattended for 4 hours or longer at 80° C., contractile force in any one or more of an absorption axis direction (MD direction) and a transmission axis direction (TD direction) may be from 3 N to 10 N. Satisfying the above-mentioned range may minimize crack occurrences on the polarizer during thermal shock. Herein, the time of being left unattended may be 4 hours or 5 hours.

In one embodiment of the present specification, when leaving the polarizing plate unattended for 4 hours or longer at 80° C., contractile force in an absorption axis direction (MD direction) is from 7 N to 9 N. Satisfying the above-mentioned range may minimize crack occurrences on the polarizer during thermal shock.

In one embodiment of the present specification, when leaving the polarizing plate unattended for 4 hours or longer at 80° C., contractile force in a transmission axis direction (TD direction) is from 4 N to 9 N. Satisfying the above-mentioned range may minimize crack occurrences on the polarizer during thermal shock.

As for the contractile force, contractile force in an MD direction or a TD direction is measured using a dynamic mechanical analyzer (DMA Q800, TA Instruments) by cutting the polarizing plate into a size of 2 mm (transmission axis direction)×50 mm (absorption axis direction), employing a gauge length of 15 mm, and leaving the specimen still for 4 hours or longer at 80° C. in an isothermal state. Herein, a minimum load is measured over a thickness direction of the polarizer in order to maintain the polarizing plate flat before the measurement.

In one embodiment of the present specification, the polarizing plate satisfies the following Equation A. When the polarizing plate satisfies the following Equation A, a difference in the contractile force depending on each region of the polarizing plate is small, which is advantageous in terms of being usable in a large image display device.

$\begin{matrix} {0.01 \leq \frac{L_{c} - L_{e}}{L_{i}} \leq 1} & \left\lbrack {{Equation}\mspace{14mu} A} \right\rbrack \end{matrix}$

In Equation A,

L_(c) is contractile force of a region corresponding to a circle area with a diameter of 1 cm having the center of the polarizing plate as the origin,

L_(e) is polarizing plate contractile force of a region corresponding to a circle area with a diameter of 1 cm adjoining two edge portions meeting at each vertex of the polarizing plate, and

L_(i) is average contractile force in an absorption axis direction (MD direction) or a transmission axis direction (TD direction) of the polarizer; or average contractile force in an absorption axis direction (MD direction) or a transmission axis direction (TD direction) of the polarizing plate.

In one embodiment of the present specification, Equation A may be represented by the following Equation A-1 or Equation A-2.

$\begin{matrix} {0.01 \leq \frac{L_{c} - L_{e}}{L_{i}} \leq 0.8} & \left\lbrack {{Equation}\mspace{14mu} A\text{-}1} \right\rbrack \\ {0.01 \leq \frac{L_{c} - L_{e}}{L_{i}} \leq 0.5} & \left\lbrack {{Equation}\mspace{14mu} A\text{-}2} \right\rbrack \end{matrix}$

In one embodiment of the present specification, methods for satisfying tensile modulus, storage modulus and a thermal expansion coefficient of the protective layer are not particularly limited, and for example, a method of comprising a photopolymerizable compound having a high glass transition temperature (Tg) in a photocurable composition for forming the protective layer, a method of increasing accumulated light intensity, and the like may be included.

In one embodiment of the present specification, the protective layer is preferably formed with a photocurable composition. When the protective layer is a curable resin layer formed from a photocurable composition as above, there are advantages in that the preparation method is simple, and furthermore, adhesion between the protective layer and the polarizer is excellent. In addition, durability of the polarizing plate may be further improved.

In one embodiment of the present specification, the photocurable composition herein is not particularly limited as long as the thermal expansion coefficient satisfies the above-mentioned range, and for example, a photocurable composition comprising an epoxy compound and an oxetane-based compound may be included. This has advantages in that heat resistance and water resistance are excellent, and the photocurable composition may be attached to the polarizer without an adhesive layer replacing an existing protective film that essentially requires an adhesive.

In one embodiment of the present specification, the photocurable composition for a polarizing plate protective layer comprises an epoxy compound and an oxetane-based compound.

In one embodiment of the present specification, the epoxy compound comprises an alicyclic epoxy compound. The alicyclic epoxy compound means a compound comprising one or more epoxidized aliphatic cyclic group. The alicyclic epoxy compound has a relatively high glass transition temperature, and therefore, is preferred in lowering a thermal expansion coefficient of the protective layer and increasing storage modulus thereof. As a result, the alicyclic epoxy compound performs a role of obtaining excellent durability under a high temperature or high humidity condition after curing.

Examples of the alicyclic epoxy compound may comprise an epoxycyclohexylmethyl epoxycyclohexane carboxylate-based compound represented by the following [Chemical Formula 1].

In Chemical Formula 1, R₁ and R₂ each independently represent hydrogen or an alkyl group.

The term alkyl group in the present specification may mean, unless particularly defined otherwise, a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms or 1 to 4 carbon atoms, and the alkyl group may be substituted by any one or more substituents, or unsubstituted.

Another example of the alicyclic epoxy compound may comprise epoxycyclohexane carboxylate-based compound of alkanediol represented by the following Chemical Formula 2.

In Chemical Formula A, R₃ and R₄ each independently represent hydrogen or an alkyl group, and n represents an integer of 2 to 20.

In addition, another example of the alicyclic epoxy compound may comprise an epoxy cyclohexylmethyl ester-based compound of dicarboxylic acid represented by the following Chemical Formula 3.

In Chemical Formula 3, R₅ and R₆ each independently represent hydrogen or an alkyl group, and p represents an integer of 2 to 20.

Another example of the alicyclic epoxy compound may comprise an epoxycyclohexylmethyl ether-based compound of polyethylene glycol represented by the following Chemical Formula 4.

In Chemical Formula 4, R₇ and R₈ each independently represent hydrogen or an alkyl group, and q represents an integer of 2 to 20.

Another example of the alicyclic epoxy compound may comprise an epoxycyclohexylmethyl ether-based compound of alkanediol represented by the following Chemical Formula 5.

In Chemical Formula 5, R₉ and R₁₀ each independently represent hydrogen or an alkyl group, and r represents an integer of 2 to 20.

Another example of the alicyclic epoxy compound may comprise a diepoxytrispiro-based compound represented by the following Chemical Formula 6.

In Chemical Formula 6, R₁₁ and R₁₂ each independently represent hydrogen or an alkyl group.

Another example of the alicyclic epoxy compound may comprise a diepoxymonospiro-based compound represented by the following Chemical Formula 7.

In Chemical Formula 7, R₁₃ and R₁₄ each independently represent hydrogen or an alkyl group.

Another example of the alicyclic epoxy compound may comprise a vinylcyclohexene diepoxide compound represented by the following Chemical Formula 8.

In Chemical Formula 8, R₁₅ represents hydrogen or an alkyl group.

Another example of the alicyclic epoxy compound may comprise an epoxycyclopentyl ether compound represented by the following Chemical Formula 9.

In Chemical Formula 9, R₁₆ and R₁₇ each independently represent hydrogen or an alkyl group.

Another example of the alicyclic epoxy compound may comprise a diepoxytricyclodecane compound represented by the following Chemical Formula 10.

In Chemical Formula 10, R₁₈ represents hydrogen or an alkyl group.

In one embodiment of the present specification, as the alicyclic epoxy compound, using an epoxycyclohexylmethyl epoxycyclohexane carboxylate compound, an epoxycyclohexane carboxylate compound of alkanediol, an epoxycyclohexylmethyl ester compound of dicarboxylic acid or an epoxycyclohexylmethyl ether compound alkanediol is preferred more specifically, and one or more selected from the group consisting of an ester compound of 7-oxabicyclo[4,1,0]heptane-3-carboxylic acid and (7-oxa-bicyclo[4,1,0]hepto-3-yl)methanol (compound that R₁ and R₂ are hydrogen in Chemical Formula 1); an ester compound of 4-methyl-7-oxabicyclo[4,1,0]heptane-3-carboxylic acid and (4-methyl-7-oxa-bicyclo[4,1,0]hepto-3-yl)methanol (compound that R₁ is 4-CH₃ and R₂ is 4-CH₃ in Chemical Formula 1); an ester compound of 7-oxabicyclo[4,1,0]heptane-3-carboxylic acid and 1,2-ethanediol (compound that R₃ and R₄ are hydrogen, and n is 1 in Chemical Formula 2); an ester compound of (7-oxabicyclo[4,1,0]hepto-3-yl)methanol and adipic acid (compound that R₅ and R₆ are hydrogen, and p is 2 in Chemical Formula 3); an ester compound of (4-methyl-7-oxabicyclo[4,1,0]hepto-3-yl)methanol and adipic acid (compound that R₅ and R₆ are 4-CH₃, and p is 2 in Chemical Formula 3); and an ether compound of (7-oxabicyclo[4,1,0]hepto-3-yl)methanol and 1,2-ethanediol (compound that R₉ and R₁₀ are hydrogen, and r is 1 in Chemical Formula 5) may be preferably used, however, the alicyclic epoxy compound is not limited thereto.

In one embodiment of the present specification, the epoxy compound and the oxetane-based compound have a weight ratio of 9:1 to 1:9, and a preferred weight ratio is from 9:1 to 7:3. When the weight ratio of the epoxy compound and the oxetane-based compound is as in the above-mentioned numerical range, the glass transition temperature of the composition may be maintained high, and an effect of greatly improving protective layer hardness after curing is obtained. In addition, the weight ratio satisfying the above-mentioned range has an advantage in that the protective layer has excellent storage modulus after curing.

In one embodiment of the present specification, the epoxy compound is preferably in 50 parts by weight to 90 parts by weight, and more preferably in 70 parts by weight to 90 parts by weight with respect to 100 parts by weight of the whole composition. Satisfying the above-mentioned range readily satisfies storage modulus and thermal expansion coefficient of the protective layer described above, and there are advantages in that the glass transition temperature of the whole composition is maintained high after curing, and adhesive strength of the composition for the polarizer is excellent.

In one embodiment of the present specification, the epoxy compound comprises a glycidyl ether-type epoxy compound. The glycidyl ether-type epoxy compound means an epoxy compound comprising at least one or more glycidyl ether groups.

In one embodiment of the present specification, examples of the glycidyl ether-type epoxy compound may comprise novolac epoxy, bisphenol A-based epoxy, bisphenol F-based epoxy, brominated bisphenol epoxy, n-butyl glycidyl ether, aliphatic glycidyl ether (12 to 14 carbon atoms), 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, o-cresyl glycidyl ether, nonylphenyl glycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, trimethylolpropane diglycidyl ether, trimethylolpropane polyglycidyl ether, polyethylene glycol diglycidyl ether or glycerin triglycidyl ether and the like. In addition, glycidyl ether having a ring-type aliphatic skeleton such as 1,4-cyclohexanedimethanol diglycidyl ether, a hydrogen-added compound of an aromatic epoxy compound and the like may be included as an example. Preferably, glycidyl ether having a ring-type aliphatic skeleton, and glycidyl ether having a ring-type aliphatic skeleton with preferably 3 to 20 carbon atoms, preferably 3 to 16 carbon atoms, and more preferably 3 to 12 carbon atoms may be used, however, the glycidyl ether-type epoxy compound is not limited thereto.

In one embodiment of the present specification, the epoxy compound may use a mixture of the alicyclic epoxy compound and the glycidyl ether-type epoxy compound.

In one embodiment of the present specification, when mixing the alicyclic epoxy compound and the glycidyl ether-type epoxy compound, the weight ratio is preferably from 3:1 to 1:3, and more preferably from 2:1 to 1:2.

In one embodiment of the present specification, the alicyclic epoxy compound may be included in 10% by weight to 100% by weight, preferably in 20% by weight to 80% by weight, and more preferably in 30% by weight to 70% by weight based on the total weight of the epoxy compound. Satisfying the above-mentioned numerical range has an advantage in that the composition may be effectively cured when photocuring.

In one embodiment of the present specification, the glycidyl ether-type epoxy compound may be included in 10% by weight to 60% by weight, and preferably in 30% by weight to 50% by weight based on the total weight of the epoxy compound.

In one embodiment of the present specification, the oxetane-based compound is a compound having a 4-membered ring ether in the molecule, and although not limited thereto, may comprise 3-ethyl-3-hydroxymethyloxetane, 1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]benzene, 3-ethyl-3-(phenoxymethyl)oxetane, di[(3-ethyl-3-oxetanyl)methyl]ether, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, phenol novolac oxetane and the like as an example. These oxetane compounds may be readily obtained as commercial products, and specific examples thereof may comprise aron oxetane OXT-101 (manufactured by TOAGOSEI Co., Ltd.), aron oxetane OXT-121 (manufactured by TOAGOSEI Co., Ltd.), aron oxetane OXT-211 (manufactured by TOAGOSEI Co., Ltd.), aron oxetane OXT-221 (manufactured by TOAGOSEI Co., Ltd.), aron oxetane OXT-212 (manufactured by TOAGOSEI Co., Ltd.) and the like.

In one embodiment of the present specification, the oxetane-based compound may be used either alone or as a mixture, and the content is preferably from 10 parts by weight to 50 parts by weight, and more preferably from 10 parts by weight to 30 parts by weight in 100 parts by weight of the whole composition. Satisfying the above-mentioned numerical range has advantages in that glass transition temperature and storage modulus of the whole composition may be maintained high after curing, and a protective layer having a uniform thickness may be formed by constantly maintaining viscosity.

In one embodiment of the present specification, the photocurable composition for a polarizing plate protective layer may further comprise a photoinitiator.

In one embodiment of the present specification, examples of the photoinitiator may comprise alpha-hydroxyketone-based compounds (ex. IRGACURE 184, IRGACURE 500, IRGACURE 2959, DAROCUR 1173; Ciba Specialty Chemicals (manufacturer)); phenylglyoxylate-based compounds (ex. IRGACURE 754, DAROCUR MBF; Ciba Specialty Chemicals (manufacturer)); benzyl dimethyl ketal-based compounds (ex. IRGACURE 651; Ciba Specialty Chemicals (manufacturer)); α-aminoketone-based compounds (ex. IRGACURE 369, IRGACURE 907, IRGACURE 1300; Ciba Specialty Chemicals (manufacturer)); monoacyl phosphine-based compounds (MAPO) (ex. DAROCUR TPO; Ciba Specialty Chemicals (manufacturer)); bisacyl phosphene-based compounds (BAPO) (ex. IRGACURE 819, IRGACURE 819DW; Ciba Specialty Chemicals (manufacturer)); phosphine oxide-based compounds (ex. IRGACURE 2100; Ciba Specialty Chemicals (manufacturer)); metallocene-based compounds (ex. IRGACURE 784; Ciba Specialty Chemicals (manufacturer)); iodonium salts (ex. IRGACURE 250; Ciba Specialty Chemicals (manufacturer)); mixtures of one or more thereof (ex. DAROCUR 4265, IRGACURE 2022, IRGACURE 1300, IRGACURE 2005, IRGACURE 2010, IRGACURE 2020; Ciba Specialty Chemicals (manufacturer)) and the like. One, or two or more types thereof may be used in the present disclosure, however, the use is not limited thereto.

In one embodiment of the present specification, the photoinitiator may be included in 0.01 parts by weight to 5 parts by weight with respect to 100 parts by weight of the photocurable composition for a polarizing plate protective layer. The photoinitiator being included in the content of the above-mentioned numerical range has advantages in that curing is favorably progressed and adhesion is more enhanced compared to when the photoinitiator is not included or the content does not satisfy the above-mentioned numerical range.

In one embodiment of the present specification, the photocurable composition for a polarizing plate protective layer may further comprise a cation polymerization initiator in 1 parts by weight to 5 parts by weight with respect to 100 parts by weight of the whole composition.

In one embodiment of the present specification, the photocurable composition for a polarizing plate protective layer preferably has viscosity of greater than or equal to 50 cPs and less than or equal to 200 cPs at 25° C., and, for example, the viscosity may be from 50 cPs to 130 cPs or less at 25° C. When the composition viscosity satisfies the above-mentioned numerical range, the protective layer may be formed to be thin and has low viscosity, which leads to an advantage of having excellent workability.

The viscosity is measured at room temperature (25° C.) with a No. 18 spindle using a Brookfield viscometer (manufactured by Brookfield Engineering). Herein, the amount of the composition is suitably from 6.5 mL to 10 mL, and stabilized values are measured within 5 minutes in order to avoid prolonged exposure to light.

In one embodiment of the present specification, the photocurable composition for a polarizing plate protective layer may further comprise one or more additives selected from the group consisting of a dye, a pigment, an epoxy resin, an ultraviolet stabilizer, an antioxidant, a colorant, a reinforcing agent, a filler, a defoamer, a surfactant, a photosensitizer and a plasticizer as necessary.

In one embodiment of the present specification, the additive may be included in 0.01 parts by weight to 5 parts by weight with respect to 100 parts by weight of the photocurable composition for a polarizing plate protective layer.

In one embodiment of the present specification, the method for forming the protective layer is not particularly limited, and the protective layer may be formed using methods well known in the art. For example, a method of forming a protective layer by coating the photocurable composition for a polarizing plate protective layer on one surface of the polarizer using a coating method well known in the art such as spin coating, bar coating, roll coating, gravure coating, blade coating and the like, and curing the result through ultraviolet irradiation may be used. For example, a method of irradiating ultraviolet light that is irradiation light using an ultraviolet irradiator may be used.

In one embodiment of the present specification, the ultraviolet wavelength may be from 100 nm to 400 nm, and preferably from 320 nm to 400 nm.

In one embodiment of the present specification, the light intensity of the irradiation light may be from 100 mJ/cm² to 1,000 mJ/cm², and preferably from 500 mJ/cm² to 1,000 mJ/cm².

In one embodiment of the present specification, the irradiation time of the irradiation light may be from 1 second to 10 minutes and preferably from 2 seconds to 30 seconds. Satisfying the above-mentioned irradiation time has an advantage of minimizing running wrinkle occurrences on the polarizer by preventing the excessive transfer of heat from a light source.

Protective Film

One embodiment of the present specification provides a polarizing plate having the protective layer provided on one surface of the polarizer, and the polarizing plate comprises a protective film attached on a surface opposite to the protective layer-provided surface of the polarizer by the medium of an adhesive layer, wherein the protective film has tensile modulus of 1700 MPa or greater at 25° C.

According to FIG. 2, the present specification provides a polarizing plate having the protective layer (20) provided on one surface of the polarizer (10), and a protective film (30) attached on a surface opposite to the protective layer (20)-provided surface of the polarizer (10) by the medium of an adhesive layer.

In the present specification, when the protective layer is formed on one surface of the polarizer, a separate protective film may be attached on a surface opposite to the protective layer-formed surface by the medium of an adhesive layer in order to support and protect the polarizer.

In one embodiment of the present specification, the protective film is for supporting and protecting the polarizer, and protective films made of various materials generally known in the art such as a polyethylene terephthalate (PET) film or a cycloolefin polymer (COP) film may be used. Considering optical properties, durability, economic feasibility and the like, using polyethylene terephthalate among these is particularly preferred.

In one embodiment of the present specification, the protective film may have tensile modulus of greater than or equal to 1,800 MPa and less than or equal to 10,000 MPa, preferably greater than or equal to 2,000 MPa and less than or equal to 8,000 MPa, and more preferably greater than or equal to 3,000 MPa and less than or equal to 7,000 MPa at 25° C. Satisfying the above-mentioned numerical range may increase a polarizer protecting effect of the protective film. Specifically, tearing of the polarizer caused by stress generated by shrinkage or expansion of the polarizer under a high temperature or high humidity environment may be prevented.

In one embodiment of the present specification, attaching the polarizer and the protective film may be carried out using a method of coating a polarizing plate adhesive composition on the surface of the polarizer or the protective film using a roll coater, a gravure coater, a bar coater, a knife coater, a capillary coater or the like, and then heat laminating these using a laminating roll, laminating through room temperature pressing, or irradiating UV after lamination. The polarizing plate adhesive composition will be described later.

Adhesive Layer

In one embodiment of the present specification, the adhesive layer is a cured material of an adhesive composition. A curable resin layer in which the adhesive layer is formed with a photocurable composition as above has advantages in that the preparation method is simple, and furthermore, adhesion with the protective film is excellent. In addition, durability of the polarizing plate may be further improved.

In one embodiment of the present specification, the adhesive layer has a thermal expansion coefficient of 130 ppm/K or less at 40° C. to 80° C. The thermal expansion coefficient being greater than 130 ppm/K has a problem of crack occurrences on the polarizing plate under a thermal shock environment.

In one embodiment of the present specification, the adhesive layer may have storage modulus of greater than or equal to 100 MPa and less than or equal to 1,800 MPa, preferably greater than or equal to 150 MPa and less than or equal to 1,300 MPa, and more preferably greater than or equal to 180 MPa and less than or equal to 500 MPa at 80° C. Satisfying the above-mentioned range is effective in that adhesive strength by the adhesive layer increases and the protective film is not favorably peeled off. Particularly, when the storage modulus is greater than the above-mentioned range, storage modulus is too high decreasing adhesive strength, and functions as an adhesive layer is not sufficiently fulfilled.

Storage modulus of the adhesive layer is measured through DMA after coating a photocurable composition having the same composition as the adhesive layer on a release film (for example, polyethylene terephthalate film) to a thickness of 50 μm, curing the result by irradiating ultraviolet rays under a condition of light intensity being 1000 mJ/cm² or greater, then removing the release film, and laser cutting the specimen to a certain size. Herein, the storage modulus is measured when constantly tensioning with 10% strain while, as the measurement temperature, raising the temperature up to 160° C. starting from −30° C. at a temperature raising rate of 5° C./min, and a storage modulus value at 80° C. is recorded.

In one embodiment of the present specification, the photocurable adhesive composition is not particularly limited as long as the thermal expansion coefficient satisfies the above-mentioned range, and for example, a photocurable composition comprising an epoxy compound and an oxetane-based compound may be included.

In one embodiment of the present specification, as the epoxy compound, at least one or more of an alicyclic epoxy compound and a glycidyl ether-type epoxy compound may be used, and preferably a mixture of an alicyclic epoxy compound and a glycidyl ether-type epoxy compound may be used. The glycidyl ether-type epoxy compound means an epoxy compound comprising at least one or more glycidyl ether groups.

In one embodiment of the present specification, Examples of the glycidyl ether-type epoxy compound may comprise novolac epoxy, bisphenol A-based epoxy, bisphenol F-based epoxy, brominated bisphenol epoxy, n-butyl glycidyl ether, aliphatic glycidyl ether (12 to 14 carbon atoms), 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, o-cresyl glycidyl ether, nonylphenyl glycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, trimethylolpropane diglycidyl ether, trimethylolpropane polyglycidyl ether, polyethylene glycol diglycidyl ether or glycerin triglycidyl ether and the like. In addition, glycidyl ether having a ring-type aliphatic skeleton such as 1,4-cyclohexanedimethanol diglycidyl ether, a hydrogen-added compound of an aromatic epoxy compound and the like may be included as an example. Preferably, glycidyl ether having a ring-type aliphatic skeleton, and glycidyl ether having a ring-type aliphatic skeleton with preferably 3 to 20 carbon atoms, preferably 3 to 16 carbon atoms, and more preferably 3 to 12 carbon atoms may be used, however, the glycidyl ether-type epoxy compound is not limited thereto.

In one embodiment of the present specification, when the alicyclic epoxy compound and the glycidyl ether-type epoxy compound are mixed, the weight ratio is preferably from 3:1 to 1:3, and more preferably from 2:1 to 1:2.

In one embodiment of the present specification, the alicyclic epoxy compound may be included in 10% by weight to 50% by weight, and preferably in 20% by weight to 40% by weight based on the total weight of the epoxy compound. Satisfying the above-mentioned numerical range has an advantage of effectively curing the composition when photocuring.

In one embodiment of the present specification, the glycidyl ether-type epoxy compound may be included in 10% by weight to 60% by weight, and preferably in 30% by weight to 50% by weight based on the total weight of the epoxy compound.

In one embodiment of the present specification, examples of the epoxy compound may comprise 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, a caprolactone-modified compound of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, an ester compound or caprolactone-modified compound of polyvalent carboxylic acid and 3,4-epoxycyclohexylmethyl alcohol, a silicone-based compound having an alicyclic epoxy group at the end, diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of brominated bisphenol A, a phenol novolac-type epoxy resin, a cresol novolac-type epoxy resin, a biphenyl-type epoxy resin, terephthalic acid diglycidyl ester, phthalic acid diglycidyl ester, an addition reactant of end carboxylic acid polybutadiene and a bisphenol A-type epoxy resin, dicyclopentadiene dioxide, limonene dioxide, 4-vinylcyclohexene dioxide, polyethylene glycol (repetition number 3 or higher) diglycidyl ether, polypropylene glycol (repetition number 3 or higher) diglycidyl ether, polytetramethylene glycol (repetition number 3 or higher) diglycidyl ether, hydrogen-added bisphenol A diglycidyl ether, epoxylated vegetable oil, 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, polybutadiene diglycidyl ether of both end hydroxyl groups, an inner epoxide of polybutadiene, a compound in which double bonds of a styrene-butadiene copolymer are partly epoxylated [for example “Epofriend” manufactured by Daicel Corporation], a compound in which isoprene units of a block copolymer of an ethylene-butylene copolymer and polyisoprene are partly epoxylated (for example, “L-207” manufactured by KRATON Corporation) and the like.

In one embodiment of the present specification, the adhesive composition may further comprise a curable component, and the curable component may be a compound having a (meth)acryloyl group, or a compound having a plurality of polymerizable double bonds such as a vinyl group. For example, tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, ring-type trimethylolpropane formal acrylate, dioxane glycol diacrylate, EO-modified diglycerin tetraacrylate, Aronix M-220 (manufactured by TOAGOSEI Co., Ltd.), light acrylate 1,9 ND-A (manufactured by Kyoeisha Chemical Co., Ltd.), light acrylate DGE-4A (manufactured by Kyoeisha Chemical Co., Ltd.), light acrylate DCP-A (manufactured by Kyoeisha Chemical Co., Ltd.), SR-531 (manufactured by Sartomer Co., Ltd.), CD-536 (manufactured by Sartomer Co., Ltd.) and the like may be included. In addition, as necessary, various epoxy (meth)acrylate, urethane (meth)acrylate, polyester (meth)acrylate, various (meth)acrylate-based monomers or the like may be included. Comprising the curable component has advantages of increasing a curing rate, and accomplishing high-level curing even with low light intensity.

In one embodiment of the present specification, the polarizing plate adhesive composition may further comprise a photoinitiator. Descriptions on the photoinitiator are the same as the descriptions on the photoinitiator included in the protective layer provided above.

In one embodiment of the present specification, the polarizing plate adhesive composition may further comprise one or more additives selected from the group consisting of a dye, a pigment, an epoxy resin, an ultraviolet stabilizer, an antioxidant, a colorant, a reinforcing agent, a filler, a defoamer, a surfactant, a photosensitizer and a plasticizer as necessary. Descriptions on the additives are the same as the descriptions on the additives included in the protective layer provided above.

Polarizer

In one embodiment of the present specification, as the polarizer, polarizers well known in the art, for example, films formed with polyvinyl alcohol (PVA) comprising iodine or a dichroic dye may be used. The polarizer may be prepared by dyeing a polyvinyl alcohol film with iodine or a dichroic dye, however, the preparation method thereof is not particularly limited.

In the present specification, the polarizer means a state not comprising a protective layer (or protective film), and the polarizing plate means a state comprising a polarizer and a protective layer (or protective film).

In one embodiment of the present specification, the polarizer may have a thickness of 5 μm to 40 μm, and more preferably 5 μm to 25 μm. When the polarizer thickness is smaller than the above-mentioned range, optical properties may decline, and when the thickness is larger than the above-mentioned range, the degree of polarizer shrinkage at a low temperature (approximately −30° C.) increases causing a problem in overall heat-related durability of the polarizing plate.

In one embodiment of the present specification, the polarizer is a polyvinyl alcohol-based film. The polyvinyl alcohol-based film is not particularly limited in the use as long as it comprises a polyvinyl alcohol resin or derivatives thereof. Herein, the derivatives of the polyvinyl alcohol resin may comprise, but are not limited to, a polyvinyl formal resin, a polyvinyl acetal resin and the like. Alternatively, the polyvinyl alcohol-based film may use commercially available polyvinyl alcohol-based films generally used in polarizer preparations in the art such as P30, PE30 or PE60 of Kuraray Co. Ltd., and M2000, M3000 or M6000 of Nippon Gohsei Co., Ltd.

In one embodiment of the present specification, the polyvinyl alcohol-based film has a degree of polymerization of 1,000 to 10,000, and preferably 1,500 to 5,000. When the degree of polymerization satisfies the above-mentioned range, molecular movements are free, and mixing with iodine, a dichroic dye or the like may be flexible.

Gluing Layer

In one embodiment of the present specification, the polarizing plate further comprises a gluing layer on the top of the protective layer. This is for attaching with a display device panel or an optical film such as a retardation film.

According to FIG. 3, the present specification comprises a protective layer (20) provided on one surface of the polarizer (10), a protective film (30) attached on a surface opposite to the protective layer (20)-provided surface of the polarizer (10) by the medium of an adhesive layer, and further comprises a gluing layer (40) provided on the top of the protective layer (20).

In one embodiment of the present specification, the gluing layer may be formed using various gluing agents well known in the art, and the type is not particularly limited. For example, the gluing layer may be formed using a rubber-based gluing agent, an acryl-based gluing agent, a silicone-based gluing agent, a urethane-based gluing agent, a polyvinyl alcohol-based gluing agent, a polyvinyl pyrrolidone-based gluing agent, a polyacrylamide-based gluing agent, a cellulose-based gluing agent, a vinylalkyl ether-based gluing agent and the like. Considering transparency, heat resistance and the like, using an acryl-based gluing agent is particularly preferred among these.

In one embodiment of the present specification, the gluing layer may be formed using a method of coating a gluing agent on the top of the protective layer, or may also be formed using a method of attaching a gluing sheet prepared by coating a gluing agent on a release sheet and then drying the result on the top of the protective layer.

Image Display Device

One embodiment of the present specification provides an image display device comprising the polarizing plate described above.

In one embodiment of the present specification, the polarizing plate may be useful in image display devices such as a liquid crystal display device.

In one embodiment of the present specification, the image display device comprises a liquid crystal panel; an upper polarizing plate provided on an upper surface of the liquid crystal panel; and a lower polarizing plate provided on a lower surface of the liquid crystal panel.

FIG. 4 illustrates an image display device providing a polarizing plate (100) on one surface of the liquid crystal panel (200). According to FIG. 4, one surface of the liquid crystal panel (200) and the polarizing plate (100) are glued by the medium of a gluing layer (40) of the polarizing plate (100).

In one embodiment of the present specification, the upper polarizing plate is the polarizing plate described above.

In one embodiment of the present specification, the lower polarizing plate is the polarizing plate described above.

In one embodiment of the present specification, the upper polarizing plate and the lower polarizing plate are the polarizing plate described above.

In one embodiment of the present specification, types of the liquid crystal panel are not particularly limited. For example, known panels comprising passive matrix-type panels such as a twisted nematic (TN)-type, a super twisted nematic (STN)-type, a ferroelectric (F)-type or a polymer dispersed (PD)-type; active matrix-type panels such as a two terminal-type or a three terminal-type; in plane switching (IPS)-type panels and vertical alignment (VA)-type panels may all be used. In addition, types of other constitutions forming a liquid crystal display device such as upper and lower substrates (ex. color filter substrate or array substrate) are not particularly limited as well, and constitutions known in the art may be employed without limit.

Hereinafter, the present specification will be described in more detail with reference to examples. However, the following examples are for illustrative purposes only, and the scope of the present specification is not limited thereby.

<Preparation of Photocurable Composition>

Preparation Examples A1 and A2: Preparation of Protective Layer Composition not Comprising Acrylate Group

Photocurable Composition A1 was prepared by adding 3 parts by weight of Irgacure 250 as a photoinitiator and 1 parts by weight of ESACURE ITX as a photosensitizer to 100 parts by weight of a photocurable composition comprising 80 parts by weight of 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate (product name Celloxide-2021) and 20 parts by weight of 3-ethyl-3-[(3-ethyloxetan-3-yl)methoxymethyl]oxetane (TOAGOSEI Co., Ltd. aron oxetane OXT-221).

In the same manner, Composition A2 having a composition of the following Table 1 was prepared. The content of the photoinitiator and the content of the photosensitizer are based on the total weight of the remaining epoxy compound and oxetane compound after excluding the photoinitiator and the photosensitizer.

TABLE 1 Category Epoxy Compound Glycidyl Alicyclic Ether-Type Epoxy Epoxy Oxetane Photo- Compound Compound Compound Photoinitiator sensitizer Product Name ESCURE CEL2021P CHDMDGE OXT-221 IRG-250 ITX Compo- 80 — 20 3 1 sition A1 Compo- 42 28 30 3 1 sition A2 *CEL2021P: 3,4-epoxycyclohexylmethyl-3′,4′- epoxycyclohexane carboxylate, CHDMDGE: 1,4-cyclohexyl dimethanol diglycidyl ether OXT-221: 3-ethyl-3-[(3-ethyloxetan-3-yl)methoxymethyl]oxetane (TOAGOSEI Co., Ltd. aron oxetane OXT-221) IRG-250: iodonium salt (product name: Irgacure-250, manufactured by Ciba Specialty Chemicals)

Preparation Examples B1 to B9: Preparation of Protective Layer Composition Comprising Acrylate Group 1) Preparation Examples B1 to B8

Protective layer compositions comprising an acrylate group were prepared as in the compositions of the following Table 2. The content of the photoinitiator and the content of the photosensitizer are based on the total weight of the remaining epoxy compound, oxetane compound and acrylic compound after excluding the photoinitiator and the photosensitizer.

TABLE 2 Epoxy Oxetane Acrylic Photoinitiator Category Compound Compound Compound Irgacure Irgacure Photosensitizer Product Name C2021P OXT221 DCPDA PVEEA VEEA 250 819 ESCUREITX Preparation Composition 56 14 30 0 0 1.85 1 0.74 Example B1 B1 Preparation Composition 48 12 40 0 0 1.58 1.5 0.63 Example B2 B2 Preparation Composition 56 14 0 30 0 1.85 1 0.74 Example B3 B3 Preparation Composition 48 12 0 30 10 1.58 1.5 0.63 Example B4 B4 Preparation Composition 56 14 0 20 10 1.85 1 0.74 Example B5 B5 Preparation Composition 56 14 15 15 0 1.85 1 0.74 Example B6 B6 Preparation Composition 56 14 15 5 10 1.85 1 0.74 Example B7 B7 Preparation Composition 56 14 5 15 10 1.85 1 0.74 Example B8 B8 * DCPDA: dicyclopentadiene acrylate PVEEA: poly(2-(2-vinyloxyethoxy)ethyl acrylate) VEEA: 2-(2-vinyloxyethoxy)ethyl acrylate IRG-819: (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide)

2) Preparation Example B9

Photocurable Composition B9 was prepared by adding 3 parts by weight of IRG-819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) as a photoinitiator to 100 parts by weight of a photocurable composition comprising 80 parts by weight of 4-hydroxybutyl acrylate (manufactured by Osaka Organic Chemicals) and 20 parts by weight of tris(2-acryloyloxyethyl)isocyanurate (product name: FA-731A, manufactured by Hitachi Chemical Co., Ltd.).

Preparation Examples C1 to C3: Preparation of Adhesive Composition

Adhesive compositions were prepared as in the compositions of the following Table 3. In the following Table 3, the content of the photoinitiator and the content of the photosensitizer are based on the total weight of the remaining epoxy compound, oxetane compound and acrylic compound after excluding the photoinitiator and the photosensitizer.

TABLE 3 Category Epoxy Compound Product Ether- Name Alicyclic Type Oxetane Acrylic or Epoxy Epoxy Compound Compound Compound Compound Compound OXT- OXT- Nonanediol Photoinitiator Photosensitizer Name CEL2021P CHDMDGE 221 212 Diacrylate — ESCUREITX Compos- 30 40 20 — 10 3 1 ition (IRG- C1 250) Compos- 35 20  5 40 — 2 1 ition C2 Compos- 30 40 20 — 10 5 — ition (CPI- C3 110P) * CPI-100P: photoinitiator manufactured by San-Apro Ltd. OXT-212: 3-ethyl-3-[(2-ethylhexyloxy)methyl]oxetane (TOAGOSEI Co., Ltd. aron oxetane OXT-212)

Examples and Comparative Examples: Manufacturing of Polarizing Plate <Example 1>—Structure of Protective Film/Polarizing Plate/Protective Layer

A polarizer was prepared using a method of dyeing a dichroic dye on a polyvinyl alcohol (PVA)-based resin film, then elongating the result in a certain direction and crosslinking the result. As an adhesive layer, Photocurable Composition C1 was coated on one surface of the polarizer prepared above using a roll coater, and after laminating a PET film as a protective film, the adhesive layer was cured by irradiating ultraviolet rays. The thickness of the adhesive layer formed with the cured photocurable composition was 2 μm.

After that, on a surface opposite to the protective film-laminated surface of the polarizer, Photocurable Composition A1 was coated using a bar coater or roll coater, and a protective layer having a thickness of 6 μm was formed by irradiating ultraviolet rays to manufacture a polarizing plate. The polarizing plate has a structure in which the protective film is laminated on one surface of the polarizer by the medium of the 2 μm adhesive layer, and the protective layer is directly formed on a surface opposite to the protective film-laminated surface of the polarizer.

Example 2

A polarizing plate was manufactured in the same manner as in Example 1 except that the protective layer had a thickness of 5 μm.

Example 3

A polarizing plate was manufactured in the same manner as in Example 1 except that the protective layer had a thickness of 8 μm.

Example 4

A polarizing plate was manufactured in the same manner as in Example 1 except that the protective layer had a thickness of 10 μm.

Example 5

A polarizing plate was manufactured in the same manner as in Example 1 except that Photocurable Composition A2 was used instead of Photocurable Composition A1 as a material of the protective layer.

Example 6

A polarizing plate was manufactured in the same manner as in Example 5 except that Photocurable Composition A2 was used instead of Photocurable Composition C1 as a material of the adhesive layer.

Comparative Example 1

A polarizing plate was manufactured in the same manner as in Example 1 except that Photocurable Composition C1 was used instead of Photocurable Composition A1 as a material of the protective layer.

Comparative Example 2

A polarizing plate was manufactured in the same manner as in Example 1 except that Photocurable Composition C2 was used instead of Adhesive Composition C1 as a material of the adhesive layer.

Comparative Example 3—PET Protective Film/Adhesive Layer/PVA/Adhesive Layer/TAC Protective Film

Photocurable Composition A2 was coated on one surface of the same polarizer as used in Example 1 so as to have a thickness of 2 μm using a roll coater, and a corona-treated PET film having a thickness of 80 μm was bonded thereto. On a surface opposite to the Photocurable Composition A2-coated surface of the polarizer, Adhesive Composition C3 was coated so as to have a thickness of 1 μm using a roll coater, a TAC film (manufactured by Fuji Tekko Co., Ltd.) having a thickness of 25 μm was bonded thereto, and Photocurable Composition A2 and Adhesive Composition C3 were cured by irradiating ultraviolet rays to manufacture a polarizing plate.

Comparative Example 4

A polarizing plate was manufactured in the same manner as in Comparative Example 3 except that an acrylic film (manufactured by Riken) having a thickness of 40 μm was used instead of the TAC film.

<Comparative Example 5>—Structure of Protective Film/Polarizing Plate/Protective Layer

A polarizing plate was manufactured in the same manner as in Example 1 except that the protective layer had a thickness of 20 μm.

Comparative Example 6

A polarizing plate was manufactured in the same manner as in Example 1 except that the protective layer had a thickness of 30 μm.

Comparative Example 7 to Comparative Example 15

Polarizing plates were manufactured in the same manner as in Example 1 except that Photocurable Compositions B1 to B9 were used instead of Photocurable Composition A1 as a material of the protective layer.

Protective layer compositions and thicknesses of the polarizing plates of the examples and the comparative examples manufactured above are shown in the following Table 4.

TABLE 4 Category Layer Composition Thickness Example 1 Protective Composition A1  6 μm Layer Adhesive Layer Composition C1  2 μm Example 2 Protective Composition A1  5 μm Layer Example 3 Protective Composition A1  8 μm Layer Example 4 Protective Composition A1 10 μm Layer Example 5 Protective Composition A2  6 μm Layer Adhesive Layer Composition C1  2 μm Example 6 Protective Composition A2  6 μm Layer Adhesive Layer Composition A2  2 μm Comparative Protective Composition C1  6 μm Example 1 Layer Comparative Protective Composition A1  6 μm Example 2 Layer Adhesive Layer Composition C2  2 μm Comparative First PET 80 μm Example 3 Protective Film First Adhesive Composition A2  2 μm Layer Second Composition C3  1 μm Adhesive Layer Second TAC 25 μm Protective Film Comparative First PET 80 μm Example 4 Protective Film First Adhesive Composition A2  2 μm Layer Second Composition C3  1 μm Adhesive Layer Second Acrylic Film 40 μm Protective Film Comparative Protective Composition A1 20 μm Example 5 Layer Comparative Protective Composition A1 30 μm Example 6 Layer Comparative Protective Composition B1  6 μm Example 7 Layer Comparative Protective Composition B2  6 μm Example 8 Layer Comparative Protective Composition B3  6 μm Example 9 Layer Comparative Protective Composition B4  6 μm Example 10 Layer Comparative Protective Composition B5  6 μm Example 11 Layer Comparative Protective Composition B6  6 μm Example 12 Layer Comparative Protective Composition B7  6 μm Example 13 Layer Comparative Protective Composition B8  6 μm Example 14 Layer Comparative Protective Composition B9  6 μm Example 15 Layer

The adhesive layers of Examples 2 to 4, Comparative Example 1, and Comparative Examples 5 to 15 are an adhesive layer having a thickness of 2 μm using Adhesive Composition C1 in the same manner as in Example 1.

Experimental Example

<Method of Property Measurements>

1. Measurement of Tensile Modulus

Tensile modulus was measured through a universal testing machine (UTM) after coating the photocurable composition prepared in the preparation example on a polyethylene terephthalate film to a thickness of 100 μm, curing the result by irradiating ultraviolet rays under a condition of light intensity being 1000 mJ/cm² or greater, then removing the release film, and laser cutting the specimen to a constant 10 mm width. Herein, the tensile modulus was obtained through a stress-strain (S-S) curve obtained by constantly tensioning with a measurement length of 50 mm and a tension rate of 50 mm/min at a measurement temperature of room temperature (25° C.) The tensile modulus was obtained by multiplying the initial slope value of the S-S curve by 100.

2. Measurement of Storage Modulus

Each of the polarizing plates manufactured in the examples and the comparative examples was cut to a size of 5.3 mm width and 4.5 cm length using laser. After that, storage modulus was measured using a dynamic mechanical analyzer (DMA). The measurement mode was multi-frequency-strain, and the measurement was made while raising the temperature from −30° C. to 160° C. raised by 5° C. per 1 minute.

3. Measurement of Thermal Expansion Coefficient

The photocurable composition prepared in the preparation example was coated between release PET, and then the result was cured under the same curing condition as in the examples so that the final thickness became 50 μm. After that, the cured material separated from the release PET was cut to a size of 6 mm width and 10 mm length. After that, a thermal expansion coefficient (CTE) was measured using TMA by, while maintaining a tension load at 0.05 N, measuring changes in the length as the temperature was raised from 30° C. to 150° C. at a temperature raising rate of 5° C./min.

4. Evaluation on High Temperature Facilitation

A protective film was laminated on a polarizer using the photocurable composition prepared in the preparation example, and cured in the same manner as in the examples. After that, a polarizing plate was manufactured by coating the result on the polarizer in the same manner as in the examples and the comparative examples except that cracks were induced on the polarizer by scraping with a load of 300 g using a blunt pencil.

After that, the polarizing plate was cut to a 6 mm width and a 10 mm length, and after leaving the polarizing plate left unattended for 100 hours at 80° C., it was observed whether light leaked by the opening of cracks due to polarizer shrinkage, and the number of cracks having light leakage among the total cracks was calculated to derive a rate of crack occurrences in the polarizing plate.

In addition, the size of the polarizing plate was changed to measure a rate of crack occurrences in the polarizing plate when used in a 55 inch panel.

*Rate of crack occurrences: number of cracks having light leakage/number of total cracks×100(%)

5. Evaluation on Adhesive Strength

A protective film was laminated on a polarizer using the photocurable composition prepared in the preparation example, and cured in the same manner as in the examples. After that, peel strength between the protective film and the polarizer being 2 N/cm or greater was determined as favorable, and being less than 2 N/cm was determined as poor.

6. Analysis on Protective Layer Component

An FTIR analysis was performed on the protective layer of each of the polarizing plates of the examples and the comparative examples, and the results are shown in the following Table 5 by analyzing the peak areas at 1720 cm⁻¹, 1410 cm⁻¹ and 910 cm⁻¹. In addition, a FTIR spectrum for Comparative Example 8 is shown in FIG. 5, and an FTIR spectrum for Example 1 is shown in FIG. 6. Measurements were each made before and after curing the protective layer composition. In addition, the range of Equation 1 was measured and is shown in the following Table 5.

TABLE 5 Category Peak Area Ia (Use Peak Ie (Use Peak 1720 cm⁻¹ Intensity at Intensity at (C═O 1410 cm⁻¹, 910 cm⁻¹ Bond) Acryl) Epoxy) Equation 1 Example 1 3.38 0 0.06 1 Example 2 6.83 0 0.06 1 Comparative 8.05 0.47 0.34 0.07 Example 7 Comparative 8.46 0.61 0.03 0.05 Example 8 Comparative 7.18 0.28 0.03 0.1 Example 9 Comparative 7.29 0.38 0.02 0.05 Example 10 Comparative 7.60 0.85 0.03 0.08 Example 11 Comparative 7.00 0.28 0.03 0.1 Example 12 Comparative 7.40 0.37 0.03 0.08 Example 13 Comparative 7.16 0.33 0.03 0.08 Example 14

In Equation 1, the peak at 1720 cm⁻¹ was selected as the peak at 1740 cm⁻¹ to 1700 cm⁻¹, and the peak at 1410 cm⁻¹ was selected as the peak at 1420 cm⁻¹ to 1380 cm⁻¹, and the ratio of peak intensity at 1410 cm⁻¹ with respect to the peak intensity at 1720 cm⁻¹ was calculated as Equation 1.

In addition, in Equation 1, the peak at 1720 cm⁻¹ was selected as the peak at 1740 cm⁻¹ to 1700 cm⁻¹, and the peak at 910 cm⁻¹ was selected as the peak at 920 cm⁻¹ to 900 cm⁻¹, and the ratio of peak intensity at 910 cm⁻¹ with respect to the peak intensity at 1720 cm⁻¹ was calculated as Ie.

The peak intensity corresponds to a peak area of the FTIR spectrum. The peak area may be derived using a direct integration method. Alternatively, assuming one peak of the FTIR spectrum having Gaussian distribution, the peak was calculated by the product of the height and the half value width of the peak.

From the results, it was identified that the polarizing plate protective layers of Example 1 and Example 2 did not comprise an acrylate group, whereas the polarizing plate protective layers of Comparative Examples 7 to 14 included an acrylate group.

7. Test on Polarizing Plate Contractile Force

Contractile force of the polarizing plate of Example 1 was tested. As for the contractile force, contractile force in an MD direction or a TD direction was measured using a dynamic mechanical analyzer (DMA Q800, TA Instruments) by cutting the polarizing plate into a size of 2 mm (transmission axis direction)×50 mm (absorption axis direction), employing a gauge length of 15 mm, and leaving the specimen still for 4 hours or longer at 80° C. in an isothermal state. Herein, a minimum load was measured over a thickness direction of the polarizer in order to maintain the polarizing plate flat before the measurement.

The measurements were repeated 8 times, and the results are shown in the following Table 6. Average contractile force in the MD direction and the TD direction were 8.03 N and 6.62 N, respectively.

TABLE 6 Category Contractile Force (Unit: N) MD Direction TD Direction 1 Time 7.9 8.09 2 Times 7.73 8.28 3 Times 7.9 8.09 4 Times 7.73 8.28 5 Times 8.12 6.45 6 Times 8.11 3.96 7 Times 9.06 6.44 8 Times 7.58 3.4 Average 8.03 6.62

<Experimental Results Depending on Inclusion of Acrylate in Protective Layer>

A durability/heat resistance test and an adhesive strength test depending on the inclusion of acrylate in the protective layer were performed, and the results are shown in the following Table 7.

From these results, it was identified that high temperature durability and adhesive strength were excellent when the polarizing plate protective layer did not comprise an acrylate group (Examples 1 and 2) compared to when the polarizing plate protective layer included an acrylate group (Comparative Examples 7 to 14).

In other words, by the polarizing plate protective layers of the examples comprising an epoxy compound and an oxetane compound instead of an acrylic compound, a polarizer protecting effect obtained by the protective layer is excellent, which leads to an advantage of minimizing crack occurrences on the polarizer under a high temperature environment even when contractile force of the polarizing plate or the polarizer is large.

TABLE 7 Category Rate of Crack Occurrences as Result of Evaluation on High Temperature Adhesive Facilitation Strength (Unit Size) Test Example 1  0% Favorable Example 2 10% Favorable Comparative Example 7 65% Poor Comparative Example 8 80% Poor Comparative Example 9 50% Poor Comparative Example 10 80% Poor Comparative Example 11 70% Poor Comparative Example 12 50% Poor Comparative Example 13 70% Poor Comparative Example 14 70% Poor

<Test on Yellowing>

A sample was prepared to test yellowing caused by lamination of the protective layer of Example 1. Specifically, Photocurable Composition A1 that is the same as the composition used for forming the protective layer of Example 1 was coated on a TAC film (manufactured by Fuji Tekko Co., Ltd., thickness 25 μm) using a bar coater or a roll coater, and the result was irradiated with ultraviolet rays of 1,000 mJ/cm² using an ultraviolet irradiator to form a protective layer having a thickness of 6 μm. After that, the sample was left unattended for 48 hours under a condition of 25° C. temperature and 40% relative humidity (RH), and yellowness (b*) of the polarizing plate was measured using a ray spectrometer (V-7100, manufactured by JASCO International Co., Ltd.). For accuracy, the measurement was repeated 3 times, and an average value was calculated.

For the remaining examples and comparative examples, yellowness was measured in the same manner, and the results are summarized in the following Table 8.

Yellowness of the polarizing plate and the polarizer before the protective layer lamination (Ybi) was from 2.3 to 2.4.

TABLE 8 Category Yellowness of Polarizing Plate Protective (Ybf) after Change in Layer Being Left Yellowness Thickness Unattended (ΔYp = Ybf − Ybi) Example 1  6 μm 3.003 0.641 Example 2  5 μm 2.932 0.542 Example 3  8 μm 3.112 0.75 Example 4 10 μm 3.275 0.913 Example 5  6 μm 2.737 0.347 Comparative 20 μm 3.774 1.384 Example 5 Comparative 30 μm 4.351 1.989 Example 6

From the results, it was identified that, in Comparative Examples 5 and 6 having a protective layer thickness of greater than 10 μm, yellowness greatly increased even when the protective layer composition is the same as in Examples 1 to 4.

<Experimental Results Depending on Protective Layer Composition>

The compositions of the examples and the comparative examples, and experimental results thereon are as shown in the following Table 9.

TABLE 9 Category Rate of @ 80° C. Crack Thermal Occurrences Layer Expansion @ 25° C. @ 80° C. on Classifi- Coefficient Tensile Storage Polarizing cation (ppm/K) Modulus Modulus Plate Example 1 Protective 82.33 2200 MPa 2500 MPa 0% Layer Adhesive 130.89  900 MPa  800 MPa Layer Example 2 Protective 82.33 2200 MPa 2500 MPa 5% Layer Adhesive 130.89  900 MPa  800 MPa Layer Example 3 Protective 82.33 2200 MPa 2500 MPa 0% Layer Adhesive 130.89  900 MPa  800 MPa Layer Example 4 Protective 82.33 2200 MPa 2500 MPa 0% Layer Adhesive 130.89  900 MPa  800 MPa Layer Example 5 Protective 99.87 2000 MPa 1900 MPa 10% Layer Adhesive 130.89  900 MPa  800 MPa Layer Example 6 Protective 99.87 2000 MPa 1900 MPa 5% Layer Adhesive 99.87 2000 MPa 1900 MPa Layer Comparative Protective 130.89  900 MPa  800 MPa 50% Example 1 Layer Adhesive 130.89  900 MPa  800 MPa Layer Comparative Protective 130.89  900 MPa  800 MPa 100% Example 2 Layer Adhesive 1063.6  50 MPa  70 MPa Layer Comparative Protective 1,000 or —(Not 300 100% Example 15 Layer Greater Performed) MPa or Less Adhesive 130.89 900 MPa  800 MPa Layer

It was identified that, in the polarizing plates according to Examples 1 to 6, the rate of crack occurrences on the polarizing plate was within 10%, whereas, in the polarizing plates according to Comparative Examples 1, 2 and 15, a number of cracks occurred on the polarizing plate. Examples 1 to 6 directly forming a protective layer on the polarizer exhibited excellent results with almost no crack occurrences on the polarizing plate while having a thin protective layer (5 μm to 10 μm). This is due to the fact that the protective layer had a low thermal expansion coefficient, and excellent tensile modulus and storage modulus, and thereby effectively suppressed polarizer expansion or shrinkage at a high temperature.

On the other hand, it was identified that, in the polarizing plates according to Comparative Examples 1, 2 and 15, the protective layer directly formed on the polarizer had a high thermal expansion coefficient, and was not able to suppress polarizer expansion or shrinkage at a high temperature, which resulted in crack occurrences on the polarizer.

Particularly, the polarizing plate of Comparative Example 15 included an acrylic compound in the protective layer, and in this case, it was identified that a number of cracks occurred based on the evaluation on high temperature facilitation since the thermal expansion coefficient of the protective layer was too high (1,000 ppm/K or greater), and the storage modulus was low (300 MPa or less).

<Experimental Results Depending on Polarizing Plate Lamination Structure>

The following Table 10 compares the polarizing plate having a structure of ‘protective film/adhesive layer/PVA/protective layer’ (Examples 1 to 6) and the polarizing plate having a structure of ‘protective film/adhesive layer/PVA/adhesive layer/protective film’ (Comparative Examples 3 and 4), and compares the protective layer directly formed on the polarizer of Examples 1 to 6 and the protective film formed by the medium of the adhesive layer on the polarizing plate of Comparative Examples 3 and 4 in terms of their materials and properties.

TABLE 10 Category Rate of 80° C. Crack Thermal 80° C. Occurrence Expansion Storage on Thickness Coefficient Modulus Polarizing (μm) (ppm/K) (Mpa) Plate Example 1 Protective 6 82.33 2500  0% Layer Example 2 Protective 5 82.33 2500  5% Layer Example 3 Protective 8 82.33 2500  0% Layer Example 4 Protective 10 82.33 2500  0% Layer Example 5 Protective 6 99.87 1900  10% Layer Example 6 Protective 6 99.87 1900  5% Layer Comparative Protective 25 88 1800  80% Example 3 Film Adhesive 1 223 700 Layer Comparative Protective 40 83 1900 80% Example 4 Film Adhesive 1 223 700 Layer

In the polarizing plates according to Comparative Examples 3 and 4, durability decreased by the occurrences of a number of cracks on the polarizing plate although a total thickness of the adhesive layer and the protective film is large.

On the other hand, in the polarizing plates according to Examples 1 to 6, the rate of crack occurrences on the polarizing plate was low while the thickness of the protective layer directly formed on the polarizer was small of 5 μm to 10 μm.

This is due to the fact that the protective layer directly formed on the polarizer of the polarizing plates of Examples 1 to 6 had excellent storage modulus while having a low thermal expansion coefficient, and thereby effectively suppressed shrinkage or expansion of the polarizer at a high temperature even without a separate protective film.

On the other hand, in the polarizing plates according to Comparative Examples 3 and 4, the adhesive layer directly formed on the polarizer had a high thermal expansion coefficient even when the protective film had a low thermal expansion coefficient, and shrinkage or expansion of the polarizer at a high temperature was not able to be effectively suppressed. 

1. A polarizing plate comprising: a polarizer; and a protective layer is on one surface or both surfaces of the polarizer directly adjoining the polarizer, wherein the protective layer is a cured material of a photocurable composition for a polarizing plate protective layer comprising an epoxy compound and an oxetane-based compound, the protective layer had a thickness of 4 μm to 11 μm, and the following Equation 1 is satisfied in a spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer: $\begin{matrix} {0.9 \leq \frac{I_{e}}{I_{a} + I_{e}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \end{matrix}$ in Equation 1, I_(e) is a ratio of peak intensity at 920 cm⁻¹ to 900 cm⁻¹ with respect to peak intensity at 1740 cm⁻¹ to 1700 cm⁻¹ in the spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer; and I_(a) is peak intensity at 1420 cm⁻¹ to 1380 cm⁻¹ with respect to peak intensity at 1740 cm⁻¹ to 1700 cm⁻¹ in the spectrum by Fourier transform infrared spectroscopy (FTIR) of the protective layer.
 2. The polarizing plate of claim 1, wherein the protective layer has yellowness (Yp) of 1 or less.
 3. The polarizing plate of claim 1, wherein a change in yellowness (ΔYp) calculated by the following Equation 2 is 1 or less: change in yellowness: ΔYp=Ybf−Ybi  [Equation 2] in Equation 2, Ybi is yellowness of the polarizer; and Ybf is yellowness of the protective layer when leaving the polarizing plate unattended for 48 hours under a condition of 25° C. and 40% relative humidity.
 4. The polarizing plate of claim 1, wherein the protective layer has a thermal expansion coefficient of 100 ppm/K or less at 80° C.
 5. The polarizing plate of claim 1, wherein the protective layer has a glass transition temperature (Tg) of higher than or equal to 90° C. and lower than or equal to 170° C.
 6. The polarizing plate of claim 1, wherein the protective layer has a storage modulus of 1,500 MPa or greater at 80° C.
 7. The polarizing plate of claim 1, wherein the protective layer has a tensile modulus of 1,700 MPa or greater at 25° C.
 8. The polarizing plate of claim 1, wherein, when leaving the polarizing plate unattended for 4 hours or longer at 80° C., a contractile force in any one or more of an absorption axis direction (MD direction) and a transmission axis direction (TD direction) is from 3 N to 10 N.
 9. The polarizing plate of claim 1, wherein the polarizing plate satisfies the following Equation A: $\begin{matrix} {0.01 \leq \frac{L_{c} - L_{e}}{L_{i}} \leq 1} & \left\lbrack {{Equation}\mspace{14mu} A} \right\rbrack \end{matrix}$ in Equation A, L_(c) is a contractile force of a region corresponding to a circle area with a diameter of 1 cm having a center of the polarizing plate as the origin; L_(e) is a polarizing plate contractile force of a region corresponding to a circle area with a diameter of 1 cm adjoining two edge portions meeting at each vertex of the polarizing plate; and L_(i) is an average contractile force in an absorption axis direction (MD direction) or a transmission axis direction (TD direction) of the polarizer; or an average contractile force in an absorption axis direction (MD direction) or a transmission axis direction (TD direction) of the polarizing plate.
 10. The polarizing plate of claim 1, wherein the epoxy compound comprises an alicyclic epoxy compound.
 11. The polarizing plate of claim 1, wherein the epoxy compound and the oxetane-based compound have a weight ratio of 9:1 to 1:9.
 12. The polarizing plate of claim 1, comprising: wherein the protective layer is on one surface of the polarizer; and the polarizing plate further comprises a protective film attached on a surface opposite to the protective layer on the one surface of the polarizer by an adhesive layer, wherein the protective film has tensile modulus of 1700 MPa or greater at 25° C.
 13. The polarizing plate of claim 1, wherein the protective layer is on both surfaces of the polarizer.
 14. The polarizing plate of claim 1, further comprising a gluing layer on a surface of the protective layer.
 15. An image display device comprising the polarizing plate of any one of claim
 1. 